@conference {liu2019long,
	title = {Long-Term Trend of Ground-Level PM2. 5 Concentrations Over 2012-2017 in China},
	booktitle = {IGARSS 2019-2019 IEEE International Geoscience and Remote Sensing Symposium},
	year = {2019},
	pages = {7842{\textendash}7845},
	publisher = {IEEE},
	organization = {IEEE},
	author = {Liu, Ming and Zhou, Gaoxiang and Saari, Rebecca K and Li, Jonathan}
}